NARRATIVE Aspen Business Park | 414 South 17th Street, Suite 107 | Ames, Iowa 50010

DATE: September 17, 2020

TO: Story County Planning and Development

RE: Treatment Improvements Cambridge, Iowa FOX PN 2473-14A

COMMENTS:

The City of Cambridge, Iowa operates a continuous discharge aerated lagoon facility. This system treats from Cambridge, primarily originating from domestic sources. In addition, the system also treats “Inflow and Infiltration (I&I)”, which is essentially non-sewage water that leaks into the sanitary collection system from leaky pipes, surface drain connections, sump pump connections and other sources. The aerated lagoon type of treatment employed at Cambridge has no issues handling the additional flow from these I&I sources, so this is not considered to a significant problem.

With the aerated lagoon type of treatment system, wastewater is treated over a long period of time in very large earthen lagoons. Aeration is provided by mechancial blowers and a network of diffusers on the bottom of the lagoons. The aeration helps to mix the contents of the lagoons and provides oxygen to the micro-organisms that break down the waste (BOD, TSS and ammonia described later), thereby cleaning the water. After treatment, the cleaned effluent is discharged to the South Skunk River via an existing outfall pipe.

The treatment system is located on the east side of town near the South Skunk River. The original wastewater system, including collection system and controlled discharge lagoons, were constructed in the early 1970’s. One of the two original lagoons was converted to a three cell aerated lagoon in 2002. Since that time, the treatment system has performed very well; reliably and consistently meeting the effluent limitations established in the discharge permit issued by Iowa Department of Natural Resources (IDNR).

The IDNR classifies rivers and streams that receive treated wastewater from municipal wastewater treatment facilities based upon specific “designated uses”. These designated uses are determined based on field investigations and other information. After IDNR proposes the designated uses for each individual stream, the EPA must approve of them before they are formally put into place. The South Skunk River at Cambridge is designated as Class B(WW-2) and A1, and descriptions of these two designated uses are summarized below:

• Warm water - Type 2 (Class “B(WW-2)”). Waters in which flow or other physical characteristics are capable of supporting a resident aquatic community that includes a variety of native nongame fish and invertebrate species. The flow and other physical characteristics limit the maintenance of warm water game fish populations. These waters generally consist of small perennially flowing streams.

800.433.3469 | 515.233.0000 | www.foxeng.com

• Primary contact recreational use (Class “A1”). Waters in which recreational or other uses may result in prolonged and direct contact with the water, involving considerable risk of ingesting water in quantities suffcient to pose a health hazard. Such activities would include, but not be limited to, swimming, diving, water skiing, and water contact recreational canoeing.

Each designated use has specific water quality requirements associated with it. The IDNR uses the water quality standards in their calculations for determining the limits for effluent parameters for the treatment system. These limits are then enacted in the treatment facility’s National Discharge Elimination (NPDES) permit, which is issued by IDNR. With the proposed project completed, the following NPDES effluent permit limits are expected to apply to the Cambridge wastewater facility:

• Biochemical Oxygen Demand (BOD): The BOD test is a widely recognized procedure used to evaluate the organic strength of wastewater. It is also widely used to evaluate the efficiency of various treatment processes and to estimate the effects of pollution on receiving streams. This test is a measure of the quantity of dissolved oxygen required by bacteria to decompose organic materials in wastewater over a specified time period and at a specified temperature.

BOD test results are usually reported in milligrams per liter (mg/l) of oxygen consumed at the end of a five-day test period that is conducted at a constant temperature of 20 degrees C. These results are referred to as the 5-day BOD (BOD5).

The BOD5 of raw (untreated) wastewater from domestic sources will normally range from approximately 150 mg/l to 250 mg/l. Industrial discharges can cause higher or lower results. Excessive infiltration/inflow can cause lower results.

The effluent limits for BOD for the Cambridge treatment facility will be 40 mg/L (average over seven days) and 25 mg/L (average over a month).

• (TSS): The undissolved substances in wastewater that can be retained on a laboratory filter are referred to as TSS. It is a major parameter in evaluating wastewater strength and in determining efficiency of treatment processes. It is also used to estimate effects of pollution on receiving streams. Suspended solids test results are reported in terms of milligrams per liter.

The effluent limits for TSS for the Cambridge treatment facility will be 120 mg/L (average over seven days) and 80 mg/L (average over a month).

• Ammonia: Ammonia is a gas that is very soluble in water and is the form of nitrogen most responsible for toxicity effects in aquatic life. Ammonia toxicity increases with higher temperatures and higher pH values. As a result, effluent ammonia standards vary throughout the year.

The toxic impacts of ammonia are mainly based on concentration: more dilute concentrations would have lower toxic effects. IDNR has specific rules that they use to determine what concentrations of ammonia are safe to discharge. Under these rules, the effluent ammonia concentration is not required to meet the water quality standards right out of the pipe. Instead, they allow for the beneficial impact of dilution as the effluent is mixed with the stream. This

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mixing occurs in a section of the stream referred to as the “Mixing Zone”, which is typically 2,000 feet long. There are conditions which can shorten the allowed length of the Mixing Zone, such as the confluence of a perrenial stream with the river (as is the case for Cambridge - see below for more details).

Anticipated ammonia limits for Cambridge are summarized in the following table. Actual ammonia levels discharged are expected to range between 1 mg/L (summer) and 15 mg/L (winter):

Anticipated Ammonia Limitations Average Month Peak Day Month Limit, mg/L Limit, mg/L January 99.5 99.5 February 58.3 58.3 March 17.2 17.2 April 21.6 21.6 May 34.4 34.4 June 33.4 33.4 July 142.3 142.3 August 108.0 108.0 September 82.5 82.5 October 49.9 49.9 November 32.3 32.3 December 112.8 112.8

• Escherichia Coli (E. coli) Bacteria: Coliform bacteria are organisms that grow in huge numbers in the intestines of all warm blooded animals, including humans. Their presence may be indicative of the presence of disease causing pathogens.

Coliform bacteria are measured as the “most probable number” of colonies per 100 mL sample (#/100 mL). The measure of coliform bacteria in the final effluent is a means for determining effectiveness of disinfection facilities. E. Coli is a type of coliform bacteria that is tested to determine compliance with disinfection requirements.

The effluent limits for E. Coli for the Cambridge treatment facility will be 126 #/100 mL. Disinfection is only required from March 15 through October 15, as recreational use of the river would not be expected during cold weather periods.

• pH: pH is a term used to express the intensity of the acid or alkaline condition of a sample. The pH scale is usually represented as ranging from 0 to 14, with pH 7 representing absolute neutrality.

The effluent limits for pH for the Cambridge treatment facility will be 6.2 to 9.0

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Cambridge’s current NPDES discharge permit was renewed by IDNR in May 2014. The renewed permit includes new, relatively low, ammonia limits that the existing facility cannot meet. Several alternatives were considered for addressing this situation. Initially, the City planned to install a new across the South Skunk River. The river diffuser would efficiently mix the treatment plant effluent with the entire river flow, thereby rapidly diluting the ammonia concentration. By changing the discharge in this way, IDNR would increase the ammonia limits to a level that the facilty could easily meet, thereby avoiding the excessive cost of treatment upgrades.

With a height of about 1.7 feet, the river diffuser would act similarly to a low head dam. As a result, a flood study was required to document no impact on flood levels. As part of this effort, several agencies were contacted for review and comment. These included US Fish and Wildlife, IDNR Fisheries, and the IDNR River Program. IDNR Fisheries expressed concern that fish would not be able to pass the diffuser during low river flows. IDNR River Program indicated that they have been working to remove low head dams on the South Skunk River to improve recreation and safety conditions. Various options were explored for mitigating these concerns, but ultimately it was found to be difficult to address the concerns while also achieving the effluent dispersion purpose of the diffuser.

A second alternative was considered to avoid the need for a river diffuser. This alternative consists of moving the discharge point further south. The existing outfall pipe discharges just upstream of the confluence of the South Skunk River and a perennial stream. Due to the rules IDNR uses when calculating ammonia limits, this drastically shortens the length of the river that can be counted towards diluting the plant effluent (mixing zone). By moving the discharge location just downstream of the perennial stream, the mixing zone would be allowed to be set at 2,000 feet long, which is the normal standard value. When taking this into account, IDNR would increase the ammonia limits to a level that the facility can meet.

Ultimately, it was decided to move forward with relocating the outfall sewer. IDNR and the City of Cambridge agreed that this would be the best alternative for meeting discharge requirements while not impacting the safe recreational use of the river or fish movement.

Because it is slated to receive State Revolving Loan (SRF) funding, the project has gone through an extensive environmental review process. The results of this effort are summarized in the attached Environmental Information Document. The report concluded that the project would have “no significant impact”.

The outfall sewer will be constructed using excavated trench methods. It will be completely buried except at the discharge point. A concrete headwall will be installed at the discharge point to protect the pipe from flood damage, and a flap gate will be installed to serve as an animal guard and prevent backflow from the river.

The outfall sewer will be constructed on land owned by the Story County Conservation Board. The parcel is located in unincorporated Story County just outside city limits. There have been no discussions or consideration of potentially annexing the parcel into the City of Cambridge. The City and Conservation Board entered into an easement agreement to allow construction of the outfall. This easement was recorded with Story County on May 29, 2020.

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In addition to the outfall relocation, the project will include construction of a new ultraviolet light disinfection system. Cambridge’s wastewater is currently not disinfected, so this improvement will improve safety for recreational use of the river. In addition, baffle curtains will be installed in the lagoons to further improve treatment efficiency and effluent quality.

The following addresses the criteria listed in 90.04 1.:

A. Compatibility:

• The new outfall sewer will be compatible with the development and use of adjacent properties. Because it is in the floodplain, future development of any adjacent areas is extremely unlikely. Wastewater treatment effluent is normally discharged into nearby streams or rivers as proposed with this project, so this is considered to be a normal feature along waterways. Access to the area is very limited to the public, so the improvements are expected to be relatively unnoticed when complete. • The new outfall sewer will be buried. For the most part, it will not be noticeable after construction is complete. The only evidence of its existence from ground surface will be the three buried manholes and the outlet headwall structure. • The manholes will be four feet inside diameter and constructed of precast concrete per SUDAS standards. Each manhole will have a 26-inch diameter cast iron cover, which is typical for municipal sewer construction. Each cover will be bolted down to prevent removal or blow off during a flood event, and each will be installed with the top flush with ground surface. • The small outlet headwall structure will be constructed of cast in place concrete as shown in the Drawings. A very similar structure to what is proposed is shown in the following picture:

B. Transition: There are no proposed buildings or surrounding properties that will be impacted by the improvements.

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C. Traffic: It is anticipated that Cambridge Staff will access the outfall site approximately one time per year on foot (no vehicles) to observe the headwall structure and check for damage or erosion concerns. Access would be via the existing permanent easement. No other access requirements are anticipated. The Heart of Iowa Trail will not be impacted by construction of the project.

D. Parking and Loading: There will be no parking or loading requirements associated with this project.

E. Signs and Lighting: There are no signs or lighting required or planned for this project.

F. Environmental Protection:

• The project will provide improved conditions from an environmental protection standpoint for safe recreational use of the river, with improved treatment and disinfection of the wastewater. • The completed project will have no negative impacts on noise, vibration, dust, smoke, fumes, odor, glare, groundwater pollution or other undesirable, hazardous or nuisance conditions, including weeds. • The total estimated area that will be disturbed for construction of the outfall sewer is 0.58 acres, which is approximately 2% of the 28.79 parcel area. • Because the total estimated disturbed area for construction of the project is less than one acre, an NPDES General Permit No. 2 for Storm Water Discharge Associated with Industrial Activity or Construction Activities is not required. The Story County erosion control requirements of 88.05 (4) will be followed.

The anticipated schedule for the project is summarized below:

Complete Design October 2020 Public Bidding December 2020 Construction March 2021 - December 2021

The actual amount of time required for construction of the outfall sewer is estimated at four weeks. The timing of construction during the period listed above will depend on weather and the contractor’s desired schedule for the project as a whole.

No other improvements to the Cambridge Wastewater Treatment Facility are anticipated over the next five years.

______Steve Van Dyke, P.E.

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DATE 01/18 01/18 01/02/18

BY SAV SRS LAST UPDATE: DRAWN: DESIGNED: CHECKED: REVISION DATE

Blower Influent Building City of Cambridge Structure City of Cambridge 10" Outfall Menadue Development 15" South Skunk River

Aerated Cell 1 Aerated Cell 2 West Lagoon Quiescent Cell Longnecker Ames, Iowa 50010 FAX: (515) 233-0103 Phone: (515) 233-0000 414 South 17th Street, Suite 107

City of Cambridge FOX Engineering Associates, Inc. Baffle Perennial Stream Curtain Story County engineering

A Heart of Iowa Nature Trail LAYOUT NAME Story County

LAYER MNGR NAME LAYER MNGR DRAWING FILENAME DRAWING SITE CAMBRIDGE, IA 0 80' 160' CAMBRIDGE WASTEWATER TREATMENT PLANT PLOT STYLE TABLE PLOT STYLE K:\!proj\2000\2473-14A Cambridge Wastewater\Drawings\Civil\2473-14A_Base.dwg Cambridge K:\!proj\2000\2473-14A FoxGrayScale AERIAL.ctb FoxGrayScale

PROJECT NO. 2473-14A

SHEET 3.2A

PLANS OF PROPOSED IMPROVEMENTS FOR DATE 02/07/20

BY ELT ELT LAST UPDATE: DRAWN: DESIGNED: CAMBRIDGE WASTEWATER IMPROVEMENTS CHECKED: CAMBRIDGE, IA LOCATION MAP NOT TO SCALE 2020 REVISION DATE

INDEX OF SHEETS Ballard Creek

No. Description

South Skunk River Skunk South G.1 COVER SHEET/ LOCATION MAP/LEGEND X X X P.1 DETAILS P.2 OUT FALL PLAN AND PROFILE

W

SAN FM OHE UGE PROJECT LOCATION Heart of Iowa Nature Trail

LYON OSCEOLA DICKINSON EMMET KOSSUTH WINNEBAGO WORTH MITCHELL HOWARD WINNESHIEK ALLAMAKEE G SIOUX O'BRIEN CLAY PALO ALTO HANCOCK CERRO GORDO FLOYD CHICKASAW FAYETTE CLAYTON

PLYMOUTH CHEROKEE BUENA VISTA POCAHONTASHUMBOLDT WRIGHT FRANKLIN BUTLER BREMER 880 881

WEBSTER BLACKHAWK BUCHANAN DELAWARE DUBUQUE WOODBURY IDA SAC CALHOUN HAMILTON HARDIN GRUNDY

MONONA TAMA BENTON LINN JONES CRAWFORD CARROLL GREENE BOONE STORY MARSHALL JACKSON

CLINTON

HARRISON SHELBY CEDAR AUDUBON GUTHRIE Ames, Iowa 50010 DALLAS POLK JASPER POWESHIEK IOWA JOHNSON

SCOTT FAX: (515) 233-0103 Phone: (515) 233-0000

POTTAWATTAMIE CASS ADAIR MADISON WARREN MARION MAHASKA KEOKUK WASHINGTON

LOUISA

MILLS MONTGOMERY ADAMS UNION CLARKE LUCAS MONROE WAPELLO JEFFERSON

HENRY FOX Engineering Associates, Inc. 414 South 17th Street, Suite 107

DES MOINES SM FREMONT PAGE TAYLOR RINGGOLD DECATUR WAYNE APPANOOSE DAVIS VAN BUREN

LEE 1 800292 8989 R Know what'sbelow. www.iowaonecall.com Callbefore you dig. engineering

G.1 GENERAL NOTE: ALL UTILITIES ARE ONLY GENERALLY LOCATED. CONTRACTOR IS RESPONSIBLE FOR LOCATING AND EXPOSING ALL

LAYOUT NAME UTILITIES THAT MAY INTERFERE WITH CONSTRUCTION BEFORE CONSTRUCTION BEGINS.

ENGINEER: FOX ENGINEERING LAYER MNGR NAME LAYER MNGR DRAWING FILENAME DRAWING ----

414 SOUTH 17TH STREET, SUITE 107 2020 AMES, IOWA 50010 CAMBRIDGE, IA

PHONE: (515) 233-0000 COVER SHEET FAX: (515) 233-0103

Witness CAMBRIDGE WASTEWATER IMPROVEMENTS FoxGrayScale.ctb PLOT STYLE TABLE PLOT STYLE K:\!proj\2000\2473-14A Cambridge Wastewater\Drawings\Civil\2473-14A_Base.dwg Cambridge K:\!proj\2000\2473-14A

PROJECT NO. 2473-14A engineering SHEET

G.1 CAMBRIDGE WASTEWATER IMPROVEMENTS DRAWING FILENAME K:\!proj\2000\2473-14A Cambridge Wastewater\Drawings\Civil\2473-14A_Base.dwg

PLOT STYLE TABLE LAYER MNGR NAME LAYOUT NAME

FoxGrayScale.ctb P1 1'-8" #4 @ 8" TRANSV. CTR

1'-6" 8" VARIES 838.00 #4 @ 8"

2'-0" 3-6" 45° 8" 1 - 18" FLAP GATE 1" = 1'-0" OUTLET HEADWALL DETAIL #4 @ 8" LONG. CENTER #4 @ 8" HORIZ. #4 @ 8" VERT. A PLAN VIEW - SECTION 2'-8" 2'-8" 3" CLEAR

18" OUTLET GROUT 8" A A - -

8" FL=838.50 18" OUTLET 1'-8" #4 @ 8" HORIZ. (FIELD CUT DOWELS AS REQUIRED #4 @ 8" VERT. DOWEL CENTER AT 18" DIAMETER PIPE.) NORTH 841.00± #4 @ 8"

DATE REVISION BY DATE PROJECT NO.

2473-14A FOX Engineering Associates, Inc. DETAILS DESIGNED: ELT 01/20 SHEET P1 CAMBRIDGE WASTEWATER IMPROVEMENTS 414 South 17th Street, Suite 107 CAMBRIDGE, IA Ames, Iowa 50010 DRAWN: ELT 01/20 2020 Phone: (515) 233-0000 CHECKED: ---- engineering FAX: (515) 233-0103 LAST UPDATE: 02/07/20

DATE 01/20 01/20 02/07/20

BY ELT ELT

12'x22' UV 00 + DISINFECTION 1 STRUCTURE LAST UPDATE: DRAWN: DESIGNED: CHECKED:

CONNECTION RIM = 846.33 FL OUT = 842.00 [P-1] (18")

ST-2 SW-401, 48" DIA. RIM = 843.67 FL IN = 838.72 [P-2] (18") REVISION FL OUT = 838.72 [P-3] (18")

00 4

+ 3 2 +

[P-1] 100L.F. 18in. STORM @ 3.05% + [P-2] 241L.F. 18in. STORM @ 0.10%00

00

ST-1 SW-401, 48" DIA. RIM = 842.68 FL IN = 838.96 [P-1] (18") FL OUT = 838.96 [P-2] (18") DATE 00 + 5 [P-3] 183L.F. 18in. STORM @ 0.10%

MECHANICALLY REMOVE TREE TO STUMP GROUND LEVEL WITH GROUND IF REQUIRED FOR CONSTRICTION ACCESS (DO NOT REMOVE ROOTBALL)

00 + 6 ST-4 24" OUTFALL RIM = 840.71 FL IN = 838.50 [P-4] (18")

82 +

6

P-4 SW-401, 48" DIA. [P-4] 32L.F. 18in. STORM @ 0.10% RIM = 845.54 FL IN = 838.54 [P-3] (18") FL OUT = 838.53 [P-4] (18") 0 20' 40'

12" TOPSOIL STRIP ALL DISTURBED AREAS Ames, Iowa 50010 REPLACE TOPSOIL LEAVE IN A FAX: (515) 233-0103

PREPARED SEEDBED CONDITION Phone: (515) 233-0000 90% COMPACTION STANDARD PROCTOR

852 852 414 South 17th Street, Suite 107 FOX Engineering Associates, Inc.

P-4 SW-401, 48" DIA. STA 6+40.1 RIM = 845.54 FL IN = 838.54 [P-3] (18") 848 ST-2 SW-401, 48" DIA. FL OUT = 838.53 [P-4] (18") 848 ST-1 SW-401, 48" DIA. STA 4+56.7 STA 2+15.5 RIM = 843.67 engineering RIM = 842.68 FL IN = 838.72 [P-2] (18") FL IN = 838.96 [P-1] (18") FL OUT = 838.72 [P-3] (18") FL OUT = 838.96 [P-2] (18") P2

LAYOUT NAME 844 844 SEE DETAIL FOR HEAD WALL CONSTRUCTION [P-1] 100L.F. 18in. STORM @ 3.05%

840 [P-2] 241L.F. 18in. STORM @ 0.10% 840 [P-3] 183L.F. 18in. STORM @ 0.10% LAYER MNGR NAME LAYER MNGR DRAWING FILENAME DRAWING ---- 2020 [P-4] 32L.F. 18in. STORM @ 0.10%

836 836 CAMBRIDGE, IA OUT FALL PLAN AND PROFILE CAMBRIDGE WASTEWATER IMPROVEMENTS

832 832 FoxGrayScale.ctb PLOT STYLE TABLE PLOT STYLE K:\!proj\2000\2473-14A Cambridge Wastewater\Drawings\Civil\2473-14A_Base.dwg Cambridge K:\!proj\2000\2473-14A

830 830 PROJECT NO. 2473-14A

SHEET 845.54 845.84 844.99 845.70 844.21 844.13 843.63 844.14 843.64 843.68 843.75 843.68 843.56 843.42 843.47 842.96 843.20 842.81 842.63 842.57 842.55 842.68 842.45 845.74 845.15 844.53 852.54 850.22 GRADE GRADE PROFILE PROFILE STATION STATION P2 0+40 0+80 1+20 1+60 2+00 2+40 2+80 3+20 3+60 4+00 4+40 4+80 5+20 5+60 6+00 6+40 6+80 7+20 7+60 Details for the flap gate we will use are attached. This information was from an earlier project, but the same size, specifications and design will apply. The gate will designed for 20 feet of water pressure from the river.